Dynamic Interaction of Genetic Risk Factors and Cocaine Abuse in the Background of Parkinsonism - a Case Report

Background: Parkinsonism is a complex multifactorial neurodegenerative disorder, in which genetic and environmental risk factors may both play a role. Among environmental risk factors cocaine was earlier ambiguously linked to Parkinsonism. Former single case reports described Parkinsonism in chronic cocaine users, but an epidemiological study did not confirm an increased risk of Parkinson's disease. Here we report a patient, who developed Parkinsonism in young age after chronic cocaine use, in whom a homozygous LRRK2 risk variant was also detected.

Case Presentation: The patient was investigated because of hand tremor, which started after a 1.5-year period of cocaine abuse. Neurological examination suggested Parkinsonism, and asymmetrical pathology was confirmed by the dopamine transporter imaging study. The genetic investigations revealed a homozygous risk allele in the LRRK2 gene. After a period of cocaine abstinence, the patient's symptoms spontaneously regressed, and the dopamine transporter imaging also returned to near-normal.

Conclusions: This case report suggests that cocaine abuse indeed might be linked to secondary Parkinsonism and serves as an example of a potential gene-environmental interaction between the detected LRRK2 risk variant and cocaine abuse. The reversible nature of the DaTscan pathology is a unique feature of this case, and needs further evaluation, whether this is incidental or can be a feature of cocaine related Parkinsonism.